aim:the presrent study was done to evaluate and compare streptococcus mutans and sanginus bacterial count on ceramo-metallic crowns and monolithic zirconia crowns at zero and 90 days follow up period >materials and methods .Twenty healthy patients were randomly chosen according to inclusion and exclusion criteria"s and randomly distributed into two groups (n=10) according to materials of the crown. Streptococcus mutans and sanginus bacterial count (CFU/ml) were collected at zero and 90 days interval from plaque ,salvary swab and saliva collection samples.Results:No signifacnt differences between the two groups except for S.sanginus was signifcantly higher in plaque sample of zirconia crowns after 90 days follow up .Conclusions Physical nature of bacteria may affect their adherence as streptococcus sanguinius showed higher count on zirconia crowns than ceramo-metallic crowns after 90 days of follow up